1. Technical Field
The present invention relates to a phosphor preparation technique, and more particularly to a method of preparing α-SiAlON phosphors using normal pressure sintering.
2. Description of the Related Art
White tight emitting diodes (LEDs) have various advantages, such as high efficiency, long lifespan and low power consumption, and many studies have been conducted to develop next generation light sources based on such white LEDs.
Y3Al5O1.2:Ce3+ (hereinafter referred to as YAG) is a yellow phosphor, which is packaged together with a blue LED chip emitting light having a wavelength of about 460 nm and is widely applied to LEDs in the art. However, YAG has a color rendering index (CRI) of about 75%, which is too low to be applied to a light source for lighting.
Two methods are used to increase the color rendering index of YAG. In one method, green and red phosphors are packaged together with a blue LED chip. In another method, blue, green and red phosphors are packaged together with a UV LED chip which emits light having a wavelength of about 405 nm. Particularly, the UV LED chip packaged together with the RGB phosphors has higher emission intensity than that of a blue LED chip and is thus suggested as a next generation light source for lighting.
On the other hand, various nitride and oxy-nitride phosphors can absorb light having wavelengths in the range of about 390 to 460 nm and are considered to be applicable to LED products. Eu2+-doped Ca-α-SiAlON is an orange phosphor and has a crystal structure which exhibits excellent chemical and mechanical stability. It is known that SiAlON is structurally stabilized by doping Y, Li, Ca, and rare-earth elements.
As green or yellow phosphors, Ce3+ or Eu2+-doped M-α-SiAlON (M=Y, Ca) phosphors may be used. Here, it is very important for the M-α-SiAlON (M=Y, Ca) phosphors to have a single α-phase. For this reason, the Ce3+ or Eu2+-doped M-α-SiAlON phosphors have been prepared via gas pressure sintering.
However, gas pressure sintering requires a complicated process, thereby significantly increasing phosphor preparation costs.